The present invention relates to the formation of chemical watermarks on a cellulosic paper substrate and, more particularly, to a multi-functional chemical watermark that is particularly well suited for security documents. Conventional watermarking is a process whereby a paper sheet is marked with specific permanent indicia. The indicia are formed in the paper web during the papermaking process by creating a localized orientation of the paper fiber in a predetermined pattern. The localized orientation creates a faint opacity difference within the body of the paper sheet such that, upon close inspection, the indicia may be viewed in the paper sheet. The economics of conventional watermarking is such that it is only cost-effective to create conventional watermarked paper in large batches.
A number of alternative chemical watermarking procedures have been developed as an alternative to conventional watermarking. Unfortunately, these alternative chemical watermarking procedures create watermarks that fall short of the high resolution standard of the conventional watermark. Further, many of the alternative chemical watermarks are subject to excessive degradation.
Accordingly, there is a need for an alternative watermarking scheme that rivals that of the conventional high resolution graphical watermarking scheme.
This need is met by the present invention wherein a cellulosic sheet suitable for use as a security document is provided including a multi-functional transparent secure mark formed therein. In accordance with one embodiment of the present invention the secure mark comprises a transparentized portion of the substrate. The cellulosic substrate defines first and second major faces. The transparentized portion comprises a transparentizing composition applied to the cellulosic substrate in a predetermined pattern so as to define a graphical image having a relative transparency selected so as to define an area of increased transparency in the substrate. The transparentizing composition comprises a transparentizing agent and a security agent.
The security agent may comprise a photochromic agent, a thermochromic agent, a fluorescent agent, a coloring agent, a UV ink, a fragrance, or combinations thereof. The transparentizing composition may comprise a radiation-curable composition, a composition selected so as to cure upon contact with the cellulosic substrate, or another type of curable composition.
In accordance with another embodiment of the present invention, a cellulosic substrate is provided having at least one transparentized portion formed therein. The transparentized portion comprises a transparentizing composition applied to the cellulosic substrate in a predetermined pattern so as to define a graphical image having a relative transparency selected so as to define an area of increased transparency in the substrate. The transparentizing composition comprises a transparentizing agent. The transparentized portion includes a printed portion. Printed matter defining the printed portion is covered by the transparentizing composition. The printed portion may be positioned in a reduced-thickness portion of the substrate. The printed matter may comprise an amount field of a negotiable document or some other secure data field.
The cellulosic substrate may define a textured portion and the graphical image may be further defined by the textured portion. The textured portion and the transparentized portion may lie in common areas of the cellulosic substrate. The textured portion and the transparentized portion may define substantially identical boundaries and may be positioned in substantial alignment on the cellulosic substrate. The textured portion may defines a variable thickness profile across which is applied the transparentizing composition such that the area of increased transparency defines a varying transparency.
In accordance with yet another embodiment of the present invention, a cellulosic substrate is provided having at least one transparentized portion formed therein. The transparentized portion comprises a transparentizing composition applied to the cellulosic substrate in a predetermined pattern so as to define a graphical image having a relative transparency selected so as to define an area of increased transparency in the substrate. The transparentizing composition comprises at least one compound selected from compounds of the formula: 
wherein
Rxe2x80x3 is any mono- or polyfunctional organic radical;
R is H or CH3;
Rxe2x80x2 is H or xe2x80x94C(O)C(R)xe2x95x90CH2, with the proviso that xe2x80x94C(O)C(R)xe2x95x90CH2 occurs at least once;
x is an integer 0-4 and indicates the number of functional groups on Rxe2x80x3 which are reactive with ethylene or propylene oxide;
z is an integer 1-4 and may vary independently of x and n;
n is an integer 1-20 and is independent of x and z; and
wherein if any of R, Rxe2x80x2, or Rxe2x80x3 are greater than one, their identities and the number of each may be the same or different;
or 
wherein
Rxe2x80x3 is any mono- or polyfunctional organic radical;
R is H or CH3;
Rxe2x80x2 is H or xe2x80x94C(O)C(R)xe2x95x90CH2, with the proviso that xe2x80x94C(O)C(R)xe2x95x90CH2 occurs at least once;
x is an integer 0-4 and indicates the number of functional groups on Rxe2x80x3 which are reactive with ethylene or propylene oxide;
z is an integer 1-4 and may vary independently of x and n;
n is an integer 1-20 and is independent of x and z; and
Rxe2x80x2xe2x80x3 is H or a group of the formula 
wherein
R, Rxe2x80x2, and n are as defined as above,
wherein if any of R, Rxe2x80x2, Rxe2x80x3 or Rxe2x80x2xe2x80x3 are greater than one, their identities and the number of each may be the same or different.
In accordance with yet another embodiment of the present invention, a cellulosic substrate is provided having at least one transparentized portion formed therein. The transparentized portion comprises a transparentizing composition applied to the cellulosic substrate in a predetermined pattern so as to define a graphical image having a relative transparency selected so as to define an area of increased transparency in the substrate. The transparentizing composition comprises:
i) a cationic catalyzable constituent selected from a vinyl ether, 2) a polyepoxide, 3) a mixture of vinyl ethers, 4) a mixture of polyepoxides, or 5) a mixture of at least one of a vinyl ether and at least one of a polyepoxide;
ii) a free radical catalyzable constituent selected from at least one compound of the Formula: 
xe2x80x83wherein,
Rxe2x80x3 is any mono- or polyfunctional organic radical;
R is H or CH3;
Rxe2x80x2 is H or xe2x80x94C(O)C(R)xe2x95x90CH2, with the proviso that xe2x80x94C(O)C(R)xe2x95x90CH2 occurs at least once;
x is an integer 0-4 and indicates the number of functional groups on Rxe2x80x3 which are reactive with ethylene or propylene oxide;
z is an integer 1-4 and may vary independently of x and n;
n is an integer 0-20 and is independent of x and z; and
wherein if any of R, Rxe2x80x2, or Rxe2x80x3 are greater than one, their identities and the number of each may be the same or different; and
iii) a catalyst constituent selected from 1) a free radical catalyst, 2) a mixture of free radical catalysts, 3) a living cationic catalyst, 4) a mixture of living cationic catalysts, or 5) mixtures of at least one of a free radical catalyst and at least one of a living cationic catalyst.
In accordance with yet another embodiment of the present invention, a cellulosic substrate is provided having at least one transparentized portion formed therein. The transparentized portion comprises a transparentizing composition applied to the cellulosic substrate in a predetermined pattern so as to define a graphical image having a relative transparency selected so as to define an area of increased transparency in the substrate. The transparentizing composition comprises at least one monomer selected from the group consisting of acrylic esters of polyhydric alcohols, methacrylic esters of polyhydric alcohols, and vinyl esters.
In accordance with yet another embodiment of the present invention, a cellulosic substrate is provided having at least one transparentized portion formed therein. The transparentized portion comprises a transparentizing composition applied to the cellulosic substrate in a predetermined pattern so as to define a graphical image having a relative transparency selected so as to define an area of increased transparency in the substrate. The transparentizing composition comprises a polymer consisting of aliphatic monomers selected from the group consisting of acrylic esters of polyhydric alcohols, methacrylic esters of polyhydric alcohols, and vinyl esters.
Accordingly, it is an object of the present invention to enhance document security by applying images that simulate high resolution graphical watermarks but provide enhanced security at a relatively lower cost than conventional watermarks. Further, it is an object of the present invention to realize improved economies by (i) enabling the production of documents including watermark type security images on bond paper stock as opposed to premium paper stock and (ii) enabling economical customization of watermark type security images. Further, it is an object of the present invention to provide documents including a glossy or plasticized security image. Also, it is an object of the present invention to provide documents including a security image that may be conveniently enhanced in a variety of ways or that may be produced to form a tactile feel. Other objects of the present invention will be apparent in light of the description of the invention embodied herein.